For example, Japanese Unexamined Patent Application Publication No. 8-196950 (Patent Literature 1) or WO01/02099 (Patent Literature 2) discloses a gun barrel of a spray gun, which is provided with a coating material nozzle that ejects a coating material flow from a coating material ejection opening on a tip end portion of the coating material nozzle, and an air cap that surrounds the tip end portion of the coating material nozzle and defines a slit in the form of a ring shape, which ejects an air flow, between the tip end portion and the air cap.
Furthermore, the tip end portion of the coating material nozzle is formed on a tip end surface thereof with a guide wall that spreads from an inner periphery of the coating material flow ejection opening part toward a tip end side of the coating material nozzle. The guide wall is adapted to control the coating material flow ejected from the coating material flow ejection opening part. The tip end portion of the coating material nozzle is also formed on an outer peripheral surface with a plurality of air grooves that is channeled from a predetermined position on a rear end side to the guide wall. The plurality of air grooves are adapted to guide a part of the air flow to a front end side of the coating material ejection opening.
The spray gun thus configured is designed such that, when coating material is ejected from the coating material ejection opening, the air flow from a gun body is introduced to the air grooves through the slit, and then mixed by collision with the coating material flow from the coating material ejection opening, thereby increasing in gas-liquid contact area. As a result thereof, the air flow, even if it were under a low pressure, can effectively atomize the coating material flow toward a central portion thereof.
Furthermore, the air cap is formed with a plurality of side air holes disposed having the coating material ejection opening of the coating material nozzle in between. The side air holes are adapted to eject the air flow so that the air flow intersects with the coating material flow from the coating material ejection opening. As a result thereof, the coating material ejected from the coating material nozzle can form, for example, an elliptical spray pattern by the aid of a compressed air ejected from the side air holes of the air cap.